In German Pat. No. 35 10 457 a chuck of this type is described which permits automatic changing of the jaw members with the help of a jaw carrier, which releases the attachment of the jaws by operation of the control rods in the chuck during closing, replaces the replaceable jaw member with a new mounted jaw member and makes the attachment again by fresh operation of the control rods.
One end of each connecting pin is guided in a threaded passage of the jaw base and at the other end has a bolt head which engages in a lock bolt recess in the replaceable jaw member. The bolt head is formed with a lock bolt shoulder projecting out beyond the pin shaft which is smaller in a direction transverse to the pin axis and wider in a direction perpendicular to that direction.
The bolt head is insertable axially in the lock bolt recess in the rotary position of the connecting pin corresponding to the unlocked configuration and is engaged axially with its lock bolt shoulder fitting in the undercut provided in the lock bolt recess in the rotary position corresponding to the locked configuration.
Further the connecting pin has on its portion located in the jaw base, gear teeth to form a pinion and the control rod has transverse gear teeth like those of rack meshing with the teeth of the connecting pin.
The control rods are guided in a tangential direction, also transversely to the chuck axis and to the adjusting direction of the jaw base and are slidable by a push rod operable against the force of restoring spring by the jaw carrier from outside the chuck body and guided axially in the chuck body.
The control rods are engaged with the push rod by a wedgetype force transmission. Axially forcing in the push rod in the chuck body against the restoring force of the restoring spring leads to sliding of the control rods and by the connected rotation of the connecting pins to a locking or unlocking of the replaceable jaw member. On rotation of the connecting pins into their rotary positions corresponding to the locked configuration the lock bolt shoulder of the lock bolt head is positioned behind an undercut in the lock bolt recess and simultaneously clamps the replaceable jaw member against the jaw base because of the axial tightening of the connecting pin in its threaded passage.
The rotation of the connecting pin requires thus a higher force the more the connecting pins are tightened in their threaded passage so that, as a result, for the later phase of the locking process and/or for the first phase of the unlocking process especially a higher applied force is required, if the attachment of the clamp jaw members in the locked configuration is to be sufficiently stable and rigid. To produce this high applied force with the help of the jaw carrier is expensive and troublesome in practice.